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Performance of the NGX High-Resolution Multiple Collector Noble Gas Mass Spectrometer

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Article numbere2021GC009997
<mark>Journal publication date</mark>30/11/2021
<mark>Journal</mark>Geochemistry, Geophysics, Geosystems
Issue number11
Number of pages11
Publication StatusPublished
Early online date13/11/21
<mark>Original language</mark>English


This paper describes the design, setup, and performance of a new analytical system installed at Lancaster University, UK, to determine noble gas isotopes in gas samples using an NGX high-resolution multiple collector noble gas mass spectrometer. The fixed position Faraday cups are configured to simultaneously measure all nine Xe isotopes whilst permitting all other noble gases, such as He, to be analyzed in peak jumping mode. The stability, sensitivity, and reproducibility of the measurements using this new noble gas analytical system were examined by repeating runs of atmospheric air. Reproducibility of the measurements obtained from 90 and 73 air standard runs are 4.2% and 0.4% for 3He/4He and 21Ne/20Ne, respectively. There is no significant difference in the 40Ar/36Ar ratio measurements with various 40Ar abundances, suggesting good sensitivity and pressure linearity of the NGX instrument. The standard errors for 124Xe/130Xe, 126Xe/130Xe, 128Xe/130Xe, 129Xe/130Xe, 131Xe/130Xe, 132Xe/130Xe, 134Xe/130Xe and 136Xe/130Xe in 46 air measurements are 0.782%, 0.804%, 0.053%, 0.029%, 0.029%, 0.029%, 0.030%, and 0.031%, respectively. In contrast, the corresponding reference values from Basford et al. (1973) are 0.342%, 0.505%, 0.148%, 0.139%, 0.153%, 0.076%, 0.156%, and 0.138%, respectively. This suggests that multicollection measurements of Xe isotopes on Faraday cups using the NGX have higher precision than the previous results except for 124Xe and 126Xe, where low abundances affect the measurement precision. Compared to traditional peak jumping single-collector mass spectrometers, the NGX has significantly decreased analytical time in Xe analysis by allowing simultaneous measurements of all isotopes. As a consequence, high analytical precision can be achieved.